feat: teletext formatting (shaka-project#1384)

This PR adds parsing of teletext styling, and rendering of the styling in output TTML and WebVTT subtitle tracks. Beyond unit tests, I've used the sample https://drive.google.com/file/d/19ZYsoeUfH85gEilQkaAdLbPhC4CxhDEh/view?usp=sharing which has rather advanced subtitling with two separate rows at the same time, where one is left aligned and another is right aligned. This necessitates two parallel cues to be rendered. It also has some colored text. Solve shaka-project#1335. ## parse teletext styling and formatting Extend the teletext parser to parse the teletext styling and formatting. This includes translating rows into regions, calculating alignment from start and stop position of the text, and extracting text and background colors. The colors are limited to full lines. Both lines and regions are propagated in the TextSample structures. This is because the number of lines may differ from different sources. For teletext, there are 24 rows, but they are essentially always used with double height, so the number of output lines is 12 from 0 to 11. There are also corresponding regions are denoted "ttx_R", where R is an integer row number. A renderer can use either the line number or the region ID to render the text. ## ttml generation for teletext to EBU-TT-D Add support to render teletext input in EBU-TT-D (IMSC-1) format. This includes appropriate regions ttx_0 to ttx_11 signalled in the TextSamples, alignment and text and background colors. The general TTML output has been changed to always include metadata, layout, and styling nodes, even if they are empty. EBU-TT-D is detected by the presence of "ttx_?" regions in the samples. If detected, extra TTML elements will be added and the EBU-TT-D linePadding used as well. Appropriate styles for background and text colors are generated depending on the color and backgroundColor attributes in the text fragments. ## adapt WebVTT output to teletext TextSample. Teletext input generates both a region with prefix ttx_ and a floating point line number (e.g. 9.5) in the range 0 to 11.5 (due to input 0-23 as double lines). The output is adopted to drop such regions and convert the line number to an integer since the standard only used floats for percent values but not for plain line numbers.
SteveR-PMP · Apr 29, 2024 · 4b5e80d · 4b5e80d
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diff --git a/CONTRIBUTORS b/CONTRIBUTORS
@@ -54,6 +54,7 @@ Sanil Raut <sr1990003@gmail.com>
 Sergio Ammirata <sergio@ammirata.net>
 Thomas Inskip <tinskip@google.com>
 Tim Lansen <tim.lansen@gmail.com>
+Torbjörn Einarsson <torbjorn.einarsson@eyevinn.se>
 Vincent Nguyen <nvincen@amazon.com>
 Weiguo Shao <weiguo.shao@dolby.com>
 
diff --git a/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-1.m4s b/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-1.m4s
diff --git a/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-2.m4s b/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-2.m4s
diff --git a/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-3.m4s b/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-3.m4s
diff --git a/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-4.m4s b/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-4.m4s
diff --git a/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-5.m4s b/packager/app/test/testdata/segmented-ttml-mp4/bear-english-text-5.m4s
diff --git a/packager/app/test/testdata/segmented-ttml-mp4/output.mpd b/packager/app/test/testdata/segmented-ttml-mp4/output.mpd
@@ -4,7 +4,7 @@
   <Period id="0" start="PT0S">
     <AdaptationSet id="0" contentType="text" segmentAlignment="true">
       <Role schemeIdUri="urn:mpeg:dash:role:2011" value="subtitle"/>
-      <Representation id="0" bandwidth="4120" codecs="stpp" mimeType="application/mp4">
+      <Representation id="0" bandwidth="4552" codecs="stpp" mimeType="application/mp4">
         <SegmentTemplate timescale="1000" initialization="bear-english-text-init.mp4" media="bear-english-text-$Number$.m4s" startNumber="1">
           <SegmentTimeline>
             <S t="0" d="1000" r="4"/>

diff --git a/packager/app/test/testdata/segmented-ttml-text/bear-english-text-1.ttml b/packager/app/test/testdata/segmented-ttml-text/bear-english-text-1.ttml
@@ -1,6 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="">
-  <head/>
+  <head>
+    <metadata/>
+    <styling/>
+    <layout/>
+  </head>
   <body>
     <div>
       <p xml:space="preserve" begin="00:00:00.000" end="00:00:00.800" tts:textAlign="center">Yup, that's a bear, eh.</p>

diff --git a/packager/app/test/testdata/segmented-ttml-text/bear-english-text-2.ttml b/packager/app/test/testdata/segmented-ttml-text/bear-english-text-2.ttml
@@ -1,6 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="">
-  <head/>
+  <head>
+    <metadata/>
+    <styling/>
+    <layout/>
+  </head>
   <body>
     <div>
       <p xml:space="preserve" begin="00:00:01.000" end="00:00:04.700" tts:textAlign="center">He 's... um... doing bear-like stuff.</p>

diff --git a/packager/app/test/testdata/segmented-ttml-text/bear-english-text-3.ttml b/packager/app/test/testdata/segmented-ttml-text/bear-english-text-3.ttml
@@ -1,6 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="">
-  <head/>
+  <head>
+    <metadata/>
+    <styling/>
+    <layout/>
+  </head>
   <body>
     <div>
       <p xml:space="preserve" begin="00:00:01.000" end="00:00:04.700" tts:textAlign="center">He 's... um... doing bear-like stuff.</p>

diff --git a/packager/app/test/testdata/segmented-ttml-text/bear-english-text-4.ttml b/packager/app/test/testdata/segmented-ttml-text/bear-english-text-4.ttml
@@ -1,6 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="">
-  <head/>
+  <head>
+    <metadata/>
+    <styling/>
+    <layout/>
+  </head>
   <body>
     <div>
       <p xml:space="preserve" begin="00:00:01.000" end="00:00:04.700" tts:textAlign="center">He 's... um... doing bear-like stuff.</p>

diff --git a/packager/app/test/testdata/segmented-ttml-text/bear-english-text-5.ttml b/packager/app/test/testdata/segmented-ttml-text/bear-english-text-5.ttml
@@ -1,6 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <tt xmlns="http://www.w3.org/ns/ttml" xmlns:tts="http://www.w3.org/ns/ttml#styling" xml:lang="">
-  <head/>
+  <head>
+    <metadata/>
+    <styling/>
+    <layout/>
+  </head>
   <body>
     <div>
       <p xml:space="preserve" begin="00:00:01.000" end="00:00:04.700" tts:textAlign="center">He 's... um... doing bear-like stuff.</p>

diff --git a/packager/app/test/testdata/segmented-ttml-text/output.mpd b/packager/app/test/testdata/segmented-ttml-text/output.mpd
@@ -4,7 +4,7 @@
   <Period id="0" start="PT0S">
     <AdaptationSet id="0" contentType="text" segmentAlignment="true">
       <Role schemeIdUri="urn:mpeg:dash:role:2011" value="subtitle"/>
-      <Representation id="0" bandwidth="2616" mimeType="application/ttml+xml">
+      <Representation id="0" bandwidth="3048" mimeType="application/ttml+xml">
         <SegmentTemplate timescale="1000" media="bear-english-text-$Number$.ttml" startNumber="1">
           <SegmentTimeline>
             <S t="0" d="1000" r="4"/>

diff --git a/packager/media/base/text_sample.h b/packager/media/base/text_sample.h
@@ -80,6 +80,11 @@ struct TextFragmentStyle {
   std::optional<bool> underline;
   std::optional<bool> bold;
   std::optional<bool> italic;
+  // The colors could be any string that can be interpreted as
+  // a color in TTML (or WebVTT). As a start, the 8 teletext colors are used,
+  // i.e. black, red, green, yellow, blue, magenta, cyan, and white
+  std::string color;
+  std::string backgroundColor;
 };
 
 /// Represents a recursive structure of styled blocks of text.  Only one of